The present invention relates to a convergent-divergent turbojet nozzle. Such convergent-divergent nozzles, referred to in this text as CD nozzles, are generally fitted to military supersonic aircraft turbojets.
FIG. 1 shows diagrammatically a CD nozzle 1 of known type. This nozzle, of axis X, comprises a first ring of convergent flaps 2 and a second ring of divergent flaps 4. Among the convergent 2 and divergent 4 flaps, the driven flaps 2a, 4a are distinguished from the follower flaps 2b, 4b. 
The driven flaps 2a, 4a are connected to a drive mechanism 5 which is used to move them. This drive mechanism usually consists of levers, link rods, yokes, or a ring, rollers and cams. The movement of the driven flaps 2a, 4a enables the opening of the nozzle 1 to be modified to suit flight conditions, and for this reason the nozzle is said to be of variable section.
The follower flaps 2b, 4b are interposed between the driven flaps and, on either side, their lateral edges bear on the radially inner faces of the driven flaps 2a, 4a. The follower flaps are not connected to a drive mechanism and simply follow the driven flaps 2a, 4a. 
The radial direction is defined in this text as the direction perpendicular to the axis X of the nozzle, and the inner face of an element as the face of the element which is nearest the axis X.
When the turbojet is running, a stream of hot gases is pouring through the nozzle 1 from the post-combustion chamber of the turbojet. By varying the opening of the nozzle, the drive mechanism 5 of the driven flaps 2a, 4a increases or decreases the exhaust velocity of the gaseous stream at the nozzle outlet.
The temperatures of the stream of hot gases passing through the CD nozzle are generally very high, and a number of cooling systems have been developed to limit the heating up of the radially inner faces of the nozzle flaps.
U.S. Pat. No. 5,775,589 discloses a CD nozzle for a military turbojet comprising follower divergent flaps supplied with cooling air.
This air flows through the inside of each flap before escaping through perforations, termed multi-perforations, in the inner wall of the flap. A protective film of air is thus formed against the surface of this wall, limiting the exchange of heat between the latter and said hot gases.
In one particular embodiment, the driven divergent flaps are not supplied with cooling air and therefore have no multiperforations, and only means for injecting air into the throat (the narrowest cross section) of the nozzle are provided to cool these flaps. However, such means are inadequate for properly cooling the driven divergent flaps, especially in regions of these flaps remote from said throat.